Bone anchor with a curved mounting element for a dynamic stabilization and motion preservation spinal implantation system and method

ABSTRACT

A dynamic stabilization, motion preservation spinal implant system includes an anchor system, a horizontal rod system and a vertical rod system. The systems are modular so that various constructs and configurations can be created and customized to a patient.

CLAIM OF PRIORITY

This application claims benefit to U.S. Provisional Application No.60/942,162, filed Jun. 5, 2007, entitled “Dynamic Stabilization andMotion Preservation Spinal Implantation System and Method”, which isincorporated herein by reference and in its entirety.

CROSS-REFERENCES

This application relates to, and incorporates herein by reference and intheir entireties, U.S. Patent Application No. 60/801,871, filed Jun. 14,2006, entitled “Implant Positioned Between the Lamina to TreatDegenerative Disorders of the Spine,” (Attorney Docket No.SPART-01018US0);

U.S. patent application Ser. No. 11/761,006, filed Jun. 11, 2007,entitled “Implant System and Method to Treat Degenerative Disorders ofthe Spine” (Attorney Docket No. SPART-01018US1);

U.S. patent application Ser. No. 11/761,100, filed Jun. 11, 2007,entitled “Implant System and Method to Treat Degenerative Disorders ofthe Spine” (Attorney Docket No. SPART-01018US2); and

U.S. patent application Ser. No. 11/761,116, filed Jun. 11, 2007,entitled “Implant System and Method to Treat Degenerative Disorders ofthe Spine” (Attorney Docket No.

BACKGROUND OF INVENTION

The most dynamic segment of orthopedic and neurosurgical medicalpractice over the past decade has been spinal devices designed to fusethe spine to treat a broad range of degenerative spinal disorders. Backpain is a significant clinical problem and the annual costs to treat it,both surgical and medical, is estimated to be over $2 billion. Motionpreserving devices to treat back and extremity pain has, however,created a treatment alternative to fusion for degenerative disc disease.These devices offer the possibility of eliminating the long termclinical consequences of fusing the spine that is associated withaccelerated degenerative changes at adjacent disc levels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of a dynamic spinestabilization system of the invention.

FIG. 1A is a posterior view of the embodiment of FIG. 1 implanted in aspine.

FIG. 2 is a top view of the embodiment of FIG. 1.

FIG. 3 is a perspective view of an embodiment of a horizontal rod systemof the invention for use with a dynamic spine stabilization system suchas depicted in FIG. 1.

FIG. 4 is a perspective view of an alternative embodiment of ahorizontal rod system of the invention for use with a dynamic spinestabilization system such as depicted in FIG. 1.

FIG. 5 is a perspective view of an embodiment of an anchor system of theinvention for use with a dynamic spine stabilization system such asdepicted in FIG. 1.

FIG. 6 is a another perspective view of the embodiment of the anchorsystem of FIG. 5.

FIG. 7 is an exploded perspective view of an alternative embodiment ofthe anchor system of the invention for use with a dynamic spinestabilization system such as depicted in FIG. 1.

FIG. 8 is a sectioned view of a portion of embodiment of the alternativeanchor system of FIG. 7 of the invention.

FIG. 9 is a side view of the anchor system of FIG. 7 depicting a degreeof freedom of movement of the anchor system of FIG. 7.

FIG. 9A is an end view of the anchor system of FIG. 9.

FIG. 10 is a side view of the anchor system of FIG. 7 depicting anotherdegree of freedom of movement of the anchor system of FIG. 7.

FIG. 10A is an end view of the anchor system of FIG. 10.

FIG. 11 is a side view of the anchor system of FIG. 7 depicting yetanother degree of freedom of movement of the anchor system of FIG. 7.

FIG. 12 is a perspective view of yet another embodiment of the anchorsystem of the invention.

FIG. 13 is an exploded perspective view of the embodiment of the anchorsystem of the invention of FIG. 12.

FIG. 14 is a perspective view of yet another embodiment of the anchorsystem of the invention.

FIG. 15 is an exploded perspective view of the embodiment of the anchorsystem of the invention of FIG. 14.

FIG. 16 is another exploded perspective view of the embodiment of theanchor system of the invention of FIG. 14.

FIG. 17 is an exploded perspective view of another embodiment of theanchor system of the invention.

FIG. 18 is a perspective view of yet another embodiment of the anchorsystem of the invention.

FIG. 19 is a perspective view of another embodiment of a dynamic spinestabilization system of the invention with another horizontal rodsystem.

FIG. 19A is a perspective view of another horizontal rod system of theinvention as depicted in FIG. 19 and partially shown in phantom form.

FIG. 19B is an exploded perspective view of the embodiment of FIG. 19.

FIG. 19C is a side view of the embodiment of FIG. 19.

FIG. 20 is a top view of the another embodiment of the dynamic spinestabilization of the system of the invention of FIG. 19.

FIG. 20A is a top side of the embodiment depicted in FIG. 19A.

FIG. 21 is another perspective view of the embodiment of the dynamicspine stabilization of the invention of FIG. 19.

FIG. 22 is a side view the embodiment of the horizontal rod system ofthe invention as depicted in FIG. 19 configured in a closed position forimplantation.

FIG. 22A is an end view of the embodiment depicted in FIG. 22.

FIG. 23 is a side view partially in phantom form of the horizontal rodsystem of FIG. 22.

FIG. 24 is a side view of the embodiment of FIG. 22 in an open positionas used when the embodiment is deployed in a spine.

FIG. 25 is an end view of the embodiment depicted in FIG. 24.

FIG. 26 is a perspective view of yet another embodiment of thehorizontal rod system of the invention.

FIG. 27 is a side view of the embodiment of the horizontal rod system ofthe invention of FIG. 26.

FIG. 28 is a perspective view of still another embodiment of thehorizontal rod system of the invention.

FIG. 29 is a side view of the embodiment of the horizontal rod system ofthe invention of FIG. 28.

FIG. 30 is a top view of another embodiment of the horizontal rod systemof the invention as depicted in FIG. 1 with the horizontal rod system inan undeployed position ready for implantation.

FIG. 31 is a top view of the embodiment of the horizontal rod system ofFIG. 30 in a deployed position after implantation.

FIG. 32 is a side view, partially in phantom of the embodiment depictedin FIG. 30.

FIG. 33 is a side view of an alternative embodiment of the horizontalrod system of the invention.

FIG. 33A is a side view of yet another embodiment of the horizontal rodsystem of the invention.

FIG. 34 is a side view of another alternative embodiment of thehorizontal rod system of the invention.

FIG. 34A is a perspective view of yet another embodiment of thehorizontal rod system of the invention.

FIG. 34B is a side view of the embodiment of FIG. 34A.

FIG. 34C is a top view of the embodiment of FIG. 34A.

FIG. 35 is a side view of still another alternative embodiment of thehorizontal rod system of the invention.

FIG. 36 is a side view of yet another alternative embodiment of thehorizontal rod system of the invention.

FIG. 37 is a side view of another alternative embodiment of thehorizontal rod system of the invention.

FIG. 38 is a side view of another alternative embodiment of thehorizontal rod system of the invention.

FIG. 39 is a side view of yet another alternative embodiment of thehorizontal rod system of the invention.

FIG. 39A is still another embodiment of the horizontal rod system andthe anchor system of the invention.

FIG. 39B is yet another embodiment of the horizontal rod system and theanchor system of the invention.

FIG. 40 is a perspective view of another embodiment of a dynamic spinestabilization system of the invention.

FIG. 41 is a perspective view of still another embodiment of a dynamicspine stabilization system of the invention.

FIG. 42 is a side view of an embodiment of a two level dynamic spinestabilization system of the invention.

FIG. 43 is a side view of yet another embodiment of a two level dynamicspine stabilization system of the invention.

FIG. 43A is a side view of an alternative embodiment of a dynamic spinestabilization system of the invention.

FIG. 44 is a side view of an embodiment of a fusion system of theinvention.

FIG. 45 is a side view of an embodiment of a two level fusion system ofthe invention.

FIGS. 45A, 45B are perspective and side views of still another fusionsystem of an embodiment of the invention that has a transition level.

FIG. 46 is a flow chart of an embodiment of the method of the invention.

FIG. 47 is yet another embodiment of the horizontal rod system of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention include a system or implant andmethod that can dynamically stabilize the spine while providing forpreservation of spinal motion. Alternative embodiments can be used forspine fusion.

Embodiments of the invention include a construct with an anchoringsystem, a horizontal rod system that is associated with the anchoringsystem and a vertical rod system that is associated with the anchoringsystem and the horizontal rod system.

An advantage and aspect of the system is that the anchoring systemincludes a head or saddle that allows for appropriate, efficient andconvenient placement of the anchoring system relative to the spine inorder to reduce the force that is placed on the anchoring system. Theanchor system has enhanced degrees of freedom which contribute to theease of implantation of the anchor system. Accordingly, the anchorsystem is designed to isolate the head and the screw from the rest ofthe dynamic stabilization system and the forces that the rest of thedynamic stabilization system can place on the anchor system and theanchor system/bone interface. Thus, the anchor system can provide asecure purchase in the spine.

Another advantage and aspect of the system is that the horizontal rodsystem is in part comprised of a super elastic material that allows forconvenient positioning of the horizontal rod system relative to theanchor system and allows for isolation of the horizontal rod system fromthe anchor system so that less force is placed on the anchor system fromthe horizontal rod system and on the anchor system/bone interface.Accordingly, unlike prior devices the anchor system stays secure in thebone of the spine.

An aspect and advantage of the invention is the ability to maximize therange of motion of the spine after embodiments of the dynamicstabilization, motion preservation implant of the invention areimplanted in a patient. While traditional solutions to back pain includefusion, discectomy, and artificial implants that replace spinestructure, embodiments of the present invention preserve the bone andligament structure of the spine and preserve a wide range of motion ofthe spine, while stabilizing spines that were heretofore unstable due todegenerative and other spinal diseases.

Still another aspect of the invention is the preservation of the naturalmotion of the spine and the maintenance of the quality of motion as wellas the wide range of motion so that the spine motion is as close to thatof the natural spine as possible. The present embodiments of theinvention allow for the selection of a less stiff, yet dynamicallystable implant for use in a non-fusion situation. A less stiff, yetdynamically stable implant relates directly to a positive patientoutcome, including patient comfort and the quality of motion of thespine.

In another aspect of the invention, load sharing is provided by theembodiment, and, in particular, the deflection rod or loading rod of theembodiment. For embodiments of this invention, the terms “deflectionrod” and “loading rod” can be used interchangeably. Accordingly thisaspect of the invention is directed to restoring the normal motion ofthe spine. The embodiment provides stiffness and support where needed tosupport the loads exerted on the spine during normal spine motion, whichloads, the soft tissues of the spine are no longer able to accommodatesince these spine tissues are either degenerated or damaged. Loadsharing is enhanced by the ability to select the appropriate stiffnessof the deflection rod or loading rod in order to match the load sharingdesired. By selecting the appropriate stiffness of the deflection rod orloading rod to match the physiology of the patient and the loads thatthe patient places on the spine, a better outcome is realized for thepatient. Prior to implantation of the embodiment, the stiffness of theimplant of the system can be selected among a number of loading rods. Inother words, the stiffness is variable depending on the deflection rodor loading rod selected. In another aspect, the load sharing is betweenthe spine and the embodiment of the invention.

In another aspect of the invention, the deflection rod or loading rod iscantilevered. In another aspect the deflection rod or loading rod iscantilevered from a horizontal rod. In yet another aspect the deflectionrod or loading rod is cantilevered from a horizontal rod that isconnected between two anchors that are affixed to the same vertebra. Inyet another aspect the deflection rod or loading rod is about parallelto the horizontal rod in a resting position. In still a further, aspectthe deflection rod or loading rod is cantilevered from a mount on thehorizontal rod and said deflection rod or loading rod is about parallelto the horizontal rod in a resting position.

In another aspect of the invention the horizontal rod attached directlyto opposite anchors is stiff and rigid, and the cantilevered deflectionrod or cantilevered loading rod shares the load with the spine resultingfrom the motions of the body of the patient.

In another aspect of embodiments of the invention, the load beingabsorbed or carried by the embodiment is being distributed along atleast part of the length of the deflection rod or loading rod. Inanother aspect of the invention, the load being absorbed or carried bythe embodiment is distributed along at least part of the length of thehorizontal cantilevered deflection rod or horizontal cantileveredloading rod.

As the load is carried horizontally along the deflection rod or loadingrod, rather than vertically, the embodiments of the invention can bemade smaller in order to fit in more spaces relative to the spine.Advantageously, the embodiments can fit in the L5-S1 space of the spine.

An aspect of the invention is to preserve and not restrict motionbetween the pedicles of the spine through the use of appropriatelyselected horizontal and vertical rods of embodiments of the invention.

An aspect of the invention is to provide for load bearing on horizontalelements such as horizontal rods instead of vertical elements or rods,and, in particular, vertical elements that are connected between boneanchoring systems.

An aspect of the invention is the use of horizontal rods in theembodiments of the invention in order to isolate each level of theimplantation system from the other so as not to put undue force and/ortorque on anchoring systems of embodiment of the invention andassociated bone, and so as to allow customization of the implantationsystem to the need of the patient. Accordingly, an aspect of theinvention is to provide for minimized loading on the bone/implantationsystem interface. Customization, in preferred embodiments, can beachieved by the selection of the horizontal rod with the desiredstiffness and stiffness characteristics. Different materials anddifferent implant configurations enable the selection of variousstiffness characteristics.

Another aspect of the invention is the ability to control stiffness forextension, flexion, lateral bending and axial rotation, and to controlstiffness for each of these motions independently of the other motions.

An aspect of the invention is to use the stiffness and load bearingcharacteristics of super elastic materials.

Another aspect of the invention is to use super elastic materials tocustomize the implant to the motion preservation and the dynamicstabilization needs of a patient. An aspect of such embodiments of theinvention is to provide for a force plateau where motion of theimplantation system continues without placement of additional force ofthe bone anchor system, or, in other words, the bone/implantation systeminterface.

Thus, an aspect of the invention is to use the horizontal bar to offsetloading on the anchor system and on the implantation system in general.

Accordingly, an aspect of the invention is to be able to selectivelyvary the stiffness and selectively vary the orientation and directionthat the stiffness is felt by varying the structure of the implantationsystem of the invention, and, in particular, to vary the stiffness ofthe horizontal rod system of the invention.

Another aspect of embodiments of the invention is to prevent anyoff-axis implantation by allowing the implantation system to haveenhanced degrees of freedom of placement of the implant. Embodiments ofthe invention provide for off-axis placement of bone anchor or pediclescrew systems.

A further aspect of embodiments of the invention is to controlstabilized motion from micro-motion to broad extension, flexion, axialrotation, and lateral bending motions of the spine.

Yet another aspect of the embodiments of the invention is to be able torevise a dynamic stabilization implant should a fusion implant beindicated. This procedure can be accomplished by, for example, theremoval of the horizontal rods of the implantation system andreplacement of such rods with stiffer rods. Accordingly, an aspect ofthe invention is to provide for a convenient path for a revision of theoriginal implantation system, if needed.

A further aspect of the invention, due to the ease of implanting theanchoring system and the ease of affixing vertical rods to thehorizontal rods of the invention, is the ability to accommodate the bonestructure of the spine, even if adjacent vertebra are misaligned withrespect to each other.

A further aspect of the invention is that the implant is constructedaround features of the spine such as the spinous processes and, thus,such features do not need to be removed and the implant does not get inthe way of the normal motion of the spine features and the spinefeatures do not get in the way of the operation of the implant.

Another aspect of embodiments of the invention is the ability tostabilize two, three and/or more levels of the spine by the selection ofappropriate embodiments and components of embodiments of the inventionfor implantation in a patient. Further embodiments of the inventionallow for fused levels (in conjunction with, if desired, bone graphs) tobe placed next to dynamically stabilized levels with the sameimplantation system. Such embodiments of the invention enable vertebrallevels adjacent to fusion levels to be shielded by avoiding an abruptchange from a rigid fusion level to a dynamically stable, motionpreserved, and more mobile level.

Accordingly, another aspect of the embodiments of the invention is toprovide a modular system that can be customized to the needs of thepatient. Horizontal rods can be selectively chosen for the particularpatient as well the particular levels of the vertebrae of the spine thatare treated. Further, the positioning of the various selected horizontalrods can be selected to control stiffness and stability.

Another aspect of embodiments of the invention is that embodiments canbe constructed to provide for higher stiffness and fusion at one levelwhile allowing for lower stiffness and dynamic stabilization at anotheradjacent level.

Yet a further aspect of the invention is to provide for dynamicstabilization and motion preservation while preserving the bone andtissues of the spine in order to lessen trauma to the patient and to usethe existing functional bone and tissue of the patient as optimally aspossible in cooperation with embodiments of the invention.

Another object of the invention is to implant the embodiments of theinvention in order to unload force from the spinal facets and otherposterior spinal structures and also the intervertebral disk.

A further aspect of the invention is to implant the embodiment of theinvention with a procedure that does not remove or alter bone or tear orsever tissue. In an aspect of the invention the muscle and other tissuecan be urged out of the way during the inventive implantation procedure.

Accordingly, an aspect of the invention is to provide for a novelimplantation procedure that is minimally invasive.

Dynamic Stabilization, Motion Preservation System for the Spine:

A dynamic stabilization, motion preservation system 100 embodiment ofthe invention is depicted in FIG. 1 and includes an anchor system 102, ahorizontal rod system 104, and a vertical rod system 106. For theseembodiments horizontal refers to a horizontal orientation with respectto a human patient that is standing and vertical refers to a verticalorientation with respect to a patient that is standing (FIG. 1A). Aswill be more fully disclosed herein below, one embodiment for the anchorsystem 102 includes a bone screw 108 which is mounted to a head orsaddle 110. Alternatively, the bone screw 108 can be replaced by a bonehook as more fully described in U.S. Provisional Patent Application No.60/801,871, entitled “An Implant Position Between the Lamina to TreatDegenerative Disorders of the Spine,” which was filed on Jun. 14, 2006,and is incorporated herein by reference and in its entirety. Themounting of the head or saddle 110 to the bone screw 108 allows formultiple degrees of freedom in order that the bone screw 108 may beappropriately, conveniently, and easily placed in the bone of the spineand in order to assist in isolating the bone screw 108 from theremainder of the system 100 so that less force is placed on the anchorsystem 102 and on the bone screw/bone interface. Some prior art devices,which use such bone screws, have, on occasion, had the bone screwsloosen from the spine, and the present embodiment is designed to reducethe force on the bone screw and on the bone screw/bone interface.Preferably, the anchor system 102 is comprised of titanium. However,other biocompatible materials such as stainless steal and/or PEEK can beused.

In the embodiment of FIG. 1, the horizontal bar system 104 is preferablysecured through the head 110 of the anchor system 102 with a locking setscrew 112. This embodiment includes a first horizontal rod 114 and asecond horizontal rod 116. The first horizontal rod 114 has first andsecond deflection rods or loading rods 118 and 120 secured thereto. In apreferred embodiment, the first horizontal rod can be comprised oftitanium, stainless steel or PEEK or another biocompatible material, andthe first and second deflection rods or loading rods can be comprised ofa super elastic material. Preferably, the super elastic material iscomprised on Nitinol (NiTi). In addition to Nitinol or nickel-titanium(NiTi), other super elastic materials include copper-zinc-aluminum andcopper-aluminum-nickel. However, for biocompatibility, thenickel-titanium is the preferred material.

Such an arrangement allows for the horizontal rod system 104 to isolateforces placed thereon from the anchor system 102 and, thus, isolateforces that could be placed on the bone screw 108 and the bonescrew/bone interface of the spine, and, thus, prevent the loosening ofthe bone screw 108 in the spine. As shown in FIG. 1 the deflection rodsor loading rods 118 and 120, in this preferred embodiment, are mountedin the center of the first horizontal rod 114 to a mount 122.Preferably, the deflection rods or loading rods 118 and 120 are forcefit into the mount 122. Alternatively, the deflection rods or loadingrods may be screwed, glued, or laser welded to the mount 122 and tobores placed in the mount 122. Other fastening techniques are within thescope and spirit of the invention. As can be seen in FIGS. 1, 3, and 4,the first horizontal rod 114 includes first and second ridges 124, 126located on either side of the mount 122 and extend at least partiallyalong the length of the first horizontal rod 114 toward the respectiveends of the horizontal rod 114. These ridges 124, 126 add rigidity tothe mount 122 relative to the rest of the horizontal rod system 104.

As seen in FIG. 1, the deflection rods or loading rods 118, 120 have aconstant diameter extending outwardly toward the respective ends 128,130 of the deflection rods or loading rods 118, 120. Alternatively, thedeflection rods or loading rods 118, 120 can have a varying diameter asthe rods 118, 120 approach their respective ends 128, 130. Preferably,as depicted and discussed below, the rods 118 and 120 can have adecreasing diameter as the rods approach the respective ends 128, 130.The decreasing diameter allows the super elastic rods 118, 120 to bemore flexible and bendable along the length of the rods as the rodsapproach the ends 128, 130 and to more evenly distribute the load placedon the system 100 by the spine. Preferably, the diameter of thedeflection rods or loading rods continuously decreases in diameter.However, it can be understood that the diameter can decrease in discretesteps along the length, with the diameter of one step not beingcontinuous with the diameter of the next adjacent step. Alternatively,for different force and load carrying criteria the diameters of thedeflection rods or loading rods can continuously increase in diameter orcan have discreet step increases in diameter along the length of thedeflection rods or loading rods as the rods extent toward the respectiveends 128, 130. Still further, the rods can have at least one step ofdecreasing diameter and at least one step of increasing diameter in anyorder along the length of the deflection rods or loading rods as therods approach the respective ends 128, 130, as desired for the force andload carrying characteristics of the deflection rods or loading rods118, 120.

With respect to FIG. 3, for example, the horizontal rod system 104, and,in particular, the deflection rods 118, 120, share the load carried bythe spine. This load sharing is directed to restoring the normal motionof the spine. This embodiment, and, in particular, the deflection rodsor loading rods 118, 120, provide stiffness and support where needed tosupport the loads exerted on the spine during spine motion, which loads,the soft tissues of the spine are no longer able to accommodate sincethese spine tissues are either degenerated or damaged. Such load sharingis enhanced by the ability to select the appropriate stiffness of thedeflection rods or loading rods 118, 120 in order to match the loadsharing desired. By selecting the appropriate stiffness of thedeflection or loading rods, to match the physiology of the patient, andthe loads that the patient places on the spine, a better outcome isrealized by the patient. Prior to implantation, the stiffness of thedeflection or loading rods can be selected from a number of deflectionor loading rods. The stiffness is variable depending on the deflectionor load rod selected. As indicated herein, the stiffness of thedeflection or loading rod can be varied by the shape of the rod and theselection of the material. Shape variations can include diameter, taper,direction of taper, stepped tapering, and material variation can includecomposition of material, just to name a few variations.

It is to be understood that the load carried by the deflection orloading rods is distributed along at least part of the length of thedeflection or loading rods. Preferably, the load is distributed alongthe entire length of the deflection or loading rods. Further, as theload is carried horizontally and the stiffness can be varied along ahorizontal member, rather than vertically, the embodiments of theinvention can be made smaller in order to fit in more spaces relative tothe spine. Advantageously, embodiments can fit, for example, in theL5-S1 space of the spine in addition to generally less constrainedspaces such as the L4-L5 space of the spine.

With respect to the embodiment of the horizontal rod system of theinvention as depicted for example in FIG. 3, the deflection rods orloading rods 118, 120 are cantilevered from mount 122. Thus, thesedeflection rods 118, 120 have a free end and an end fixed by the mount112, which mount is located on the horizontal rod 114. As is evident inFIG. 3, the cantilevered deflection rods 118, 120 are about parallel ina rested position to the horizontal rod 114, and, in this embodiment,the horizontal rod is directly connected to the anchor systems and, inparticular, to the heads or saddles of the anchor system. Preferably,the horizontal rod 114 is stiff and rigid and, particularly, incomparison to the deflection rods. In this arrangement, the horizontalrod system and, in particular, the deflection rods 118, 120 share theload resulting from the motions of the body of the patient.

As an alternate embodiment, the second horizontal rod 116 could bereplaced with a horizontal rod 114 which has deflection rods or loadingrods (FIG. 43A). Thus, both horizontal rods would have deflection rodsor loading rods. The deflection rods or loading rods mounted on onehorizontal rod would be connected to vertical rods and the vertical rodswould be connected to deflection rods or loading rods mounted on theother horizontal rod. Such an embodiment provides for more flexibility.Further, the deflection rods or loading rods 118, 120 can have otherconfigurations and be within the spirit and scope of the invention.

Further, as can be seen in FIG. 1, the vertical rod system is comprisedof, in this embodiment, first and second vertical rods 132, 134 whichare secured to first and second connectors 136, 138 located at the ends128, 130 of the first and second deflection rods or loading rods 118,120. As will be described below, the vertical rods 132, 134 arepreferably connected in such a way as to be pivotal for purposes ofimplantation in a patient and for purposes of adding flexibility anddynamic stability to the system as a whole. These vertical rods 132, 134are preferably made of titanium. However, other bio-compatible materialscan be used. The vertical rods 132, 134 are also connected to the secondhorizontal rod 116 by being received in C-shaped mounts 140, 142 locatedon the second horizontal rods and in this embodiment, held in place byset screws 144,146. It is to be understood by one of ordinary skill inthe art that other structures can be used to connect the vertical rodsto the horizontal rods.

Preferably, the vertical rods are only connected to the horizontal rodsand not to the anchoring system 102 in order to isolate the anchorsystem 102 and, in particular, the heads 110 from stress and forces thatcould be placed on the heads, and from forces transferred to the headswhere the vertical rods connect to the heads. Thus, the system 100through the vertical and horizontal rods allow for dynamic stability,and a wide range of motion without causing undue force to be placed onthe heads of the anchor systems. These embodiments also allow for eachlevel of the spine to move as freely as possible without being undulyrestrictively tied to another level.

More lateral placement of the vertical rods toward the heads of theanchor system provides for more stiffness in lateral bending and aneasier implant approach by, for example, a Wiltse approach as describedin “The Paraspinal Sacraspinalis-Splitting Approach to the LumberSpine,” by Leon L. Wiltse et al., The Journal of Bone & Joint Surgery,Vol. 50-A, No. 5, July 1968, which is incorporated herein by reference.

The stiffness of the system 100 can preferably be adjusted by theselection of the materials and placement and diameters of the horizontaland vertical rods and also the deflection rods or loading rods. Largerdiameter rods would increase the resistance of the system 100 toflexion, extension rotation, and bending of the spine, while smallerdiameter rods would decrease the resistance of the system 100 toflexion, extension, rotation and bending of the spine. Further,continually or discretely changing the diameter of the rods such as thedeflection rods or loading rods along the length of the rods changes thestiffness characteristics. Thus, with the deflection rods or loadingrods 118, 120 tapered from the mount 122 toward the ends 128, 130, thesystem can have more flexibility in flexion and extension of the spine.Further, using a super elastic material for the horizontal rods and thevertical rods in addition to the horizontal deflection rods or loadingrods adds to the flexibility of the system 100. Further, all of thehorizontal and vertical rods, in addition to the deflection rods orloading rods, can be made of titanium or stainless steel or PEEK shoulda stiffer system 100 be required. Thus, it can be appreciated that thesystem 100 can easily accommodate the desired stiffness for the patientdepending on the materials uses, and the diameter of the materials, andthe placement of the elements of the system 100.

Should an implanted system 100 need to be revised, that can beaccomplished by removing and replacing the horizontal and/or verticalrods to obtain the desired stiffness. By way of example only, should astiffer revised system be desired, more akin to a fusion, or, in fact, afusion, then the horizontal rods having the deflection rods or loadingrods can be removed and replaced by horizontal rods having deflectionrods or loading rods made of titanium, or stainless steel, or non-superelastic rods to increase the stiffness of the system. This can beaccomplished by leaving the anchor system 102 in place and removing theexisting horizontal rods from the heads 110 and replacing the horizontalrods with stiffer horizontal rods and associated vertical rods.

FIG. 3 depicts a view of the horizontal rod 104 as previously described.In this embodiment the connectors 136, 138 are shown on the ends of thedeflection rods or loading rods 118, 120. The connectors can beforced-fitted to the deflection rods or fastened in other methods knownin the art for this material and as further disclosed below. Theconnectors 136, 138 have slits 148, 150 to aid in placing the connectorsonto the ends of the deflection rods. As is evident from FIG. 3, theconnectors 136, 138 each include upper and lower arms 160, 162 which cancapture there between the vertical rods 132, 134. The arms each includean aperture 168, 170 that can accept a pin or screw 176, 178 (FIG. 1)for either fixedly or pivotally securing the vertical rods 132, 134. Inthis embodiment the vertical rods include a head 162, 164 that can beforce fit or screwed onto the rest of the vertical rods. The headsinclude apertures 172, 174 for accepting the pins or screws 176, 178.

In order that the system 100 has as low a profile as possible andextends from the spine as little as possible, it is advantageous toplace the deflection rods or loading rods 118, 120 as close to the firsthorizontal rod 114 as possible. In order to accomplish this low profile,preferably notches 152, 154 are placed in horizontal rod 114 toaccommodate the connectors 136, 138.

Accordingly, the purpose for the notches is to provide for a horizontalrod with a low profile when implanted relative to the bones and tissuesof the spine so that there is, for example, clearance for implant andthe motion of the implant, and to keep the deflection rods or loadingrods as close as possible to the horizontal rods in order to reduce anypotential moment arm relative to the mounts on the horizontal rod.

FIG. 4 depicts another embodiment of the horizontal rod 114 withdeflection rods or loading rods 118, 120 and with difference connectors156, 158. Connectors 156, 158 each include two pairs of upper and lowerarms 160, 162 extending in opposite directions in order for eachconnector 156, 158 to mount an upper and a lower vertical rod aspresented with respect to FIG. 46. This configuration allows for a threelevel system as will be described below.

Embodiments of the Anchor System of the Invention

A preferred embodiment of the anchor system 102 invention can be seen inFIG. 5. This is similar to the anchor system 102 depicted in FIG. 1. Inparticular, this anchor system 102 includes a bone screw 108 with a head110 in the form of a U-shaped yoke 180 with arms 182, 184. As will bediscussed further, a hook, preferably with bone engaging barbs orprojections, can be substituted for the bone screw 108. The hookembodiment is further described in the above referenced and incorporatedprovisional application. The hooks are used to hook to the bone, such asthe vertebra instead of having screws anchored into the bone. Each ofthe arms 182, 814 of yoke 180 includes an aperture 186, 188 throughwhich a pin 190 can be placed. The pin 190 can be laser welded or forcefit or glued into the yoke 180, as desired. The pin 190 can be smooth orroughened as discussed below. Further, the pin 190 can be cylindrical orbe comprised of a multiple sides as shown in FIG. 7. In FIG. 7, pin 190has six sides and one or more of the accommodating apertures 186, 188can also include mating sides in order to fix the position of the pin190 in the yoke 180. A compression sphere 200 is placed over the pin190. The compression sphere 200 can have a roughened surface if desiredto assist in locking the sphere in place as described below. Thecompression sphere 200 can include one or more slits 202 to assist incompressing the sphere 200 about the pin 190. The compression sphere 200can have an inner bore that is cylindrical or with multiple sides inorder conform to and be received over the pin 190. As can be seen inFIG. 8, one or more spacer rings 204 can be used to space thecompression ring from the yoke 180 in order to assist in providing therange of motion and degrees of freedom that are advantageous to theembodiments of the invention.

Mounted about the compression sphere 200 is the head or saddle 110. Head110 in FIGS. 7, 8 is somewhat different from head 110 in FIG. 1 as willbe described below. Head 110 in FIGS. 7, 8 includes a cylindrical body206 with a lower end having an aperture 208 that can receive thecompression sphere 200. The aperture 208 can have a concave surface asdepicted in FIGS. 7, 8. Accordingly, the compression sphere 200 fitsinside of the concave surface of aperture 208 and is free to movetherein until restrained as described below. As is evident from thefigures, the lower end of the cylindrical body 206 about the aperture208 has some of the material that comprised wall 224 removed in order toaccommodate the motion of the yoke 180 of the bone screw 108.Essentially, the portion of the wall 224 adjacent to the arms 182, 184of the yoke 180 has been removed to accommodate the yoke 180 and therange of motion of the yoke.

The head 110 of the anchor system 102 includes an internal cylindricalbore 210 which is preferably substantially parallel to a longitudinalaxis of the head 110. This bore 210 is open to the aperture 208 and isopen and preferably substantially perpendicular to the distal end 212 ofthe head 110. At the distal end 212 of the head 110, the bore 210 isthreaded and can accept the set screw 112. Along the side of the head110 are defined aligned U-shaped slots that extend through the head 110from the outer surface to the bore 210. These U-shaped slots are alsoopen to the distal end 212 of the head 110 in order to have the setscrew 112 accepted by the threads of the bore 210. Located in the bore210 between the set screw 112 and the compression sphere 200 is acompressor element or cradle 220. The compressor element or cradle 220can slide somewhat in the bore 210, but the compressor element or cradle220 is restrained by a pin 222 (FIG. 7) received through the wall 224 ofthe head 110 and into the compressor element or cradle 220. Thus, thecompressor element or cradle 220, until locked into position, can movesomewhat in the bore 210.

The compressor element or cradle 220 has a generally cylindrical body sothat the compressor element 220 can fit into bore 210. An upper end 226of the compressor element 220 includes a concave surface 228. Thissurface 228 is shaped to fit the horizontal rod system 104 and, inparticular, a horizontal rod 114, 116. The lower end of the compressorelement 220 includes a concave surface 230 which can accommodate thecompression sphere 200. The lower end of the compressor element 220adjacent to the concave surface 230 has an additional concave surface232 (FIG. 8) which is used to accommodate the motion of the upper end ofthe yoke 180 as the head 110 is moved relative to the bone screw 108.The concave surfaces 228 and 230 can be roughened, if desired, to assistin locking the head 110 relative to the bone screw 108. In thisembodiment (FIGS. 5, 6) there is no top compression element or cradle(see, for example, FIGS. 7, 13) in order to reduce the profile of thehead of the anchor system.

As is evident from the figures, with the anchor system 102 assembled andwith a horizontal rod 114, 116 received in the U-shaped slot 216, theset screw can press against the horizontal rod 114, 116, whichhorizontal rod 114, 116, can press against the compressor element orcradle 220, which compressor element or cradle 220 can press against thecompression sphere 220, which compression sphere can press against thepin 190 in order to lock the horizontal rod 114, 116 relative to thehead 110 and to lock the head 110 relative to the bone screw 108. It isto be understood that all of the surfaces that are in contact, can beroughened to enable this locking, if desired. Alternatively, thesurfaces may be smooth with the force of the set screw 112 urging of theelements together and the resultant locking.

As can be seen in FIGS. 5, 6 an alternative horizontal rod 114, 116 isdepicted. This alternative horizontal rod 114, 116 includes first andsecond concave openings 234, 236 which can receive vertical rods such asvertical rods 132, 134 (FIG. 1). The horizontal rod 114, 116 issubstantially cylindrical with the areas around the concave openings234, 236 bulked up or reinforced as desired to support the forces.Additionally, threaded bores are provided adjacent to the concaveopenings 234, 236 and these bores can receive screws that have headsthat can be used to lock vertical rods in place. Alternatively, thescrews can retain short bars that project over the concave openings 234,236 in order to hold the vertical rods in place (FIG. 34). If desired,the short retaining bars can also have concave openings that conform tothe shape of, and receive at least part of, the vertical rods in orderto retain the vertical rods in place with the system 100 implanted in apatient.

Turning again to FIGS. 1, 2, 5, 6, the head 110 depicted is a preferredembodiment and is somewhat different from the head 110 as seen in FIG.8. In particular the head body 206, the outer surface 218 of the headand the head wall 224, have been configured in order to prevent splayingof the head 110 when the set screw 112 locks the anchor system 102 asexplained above. As seen in FIGS. 1, 2, the head 110 and, in particular,the wall 224 is reinforced about the U-shaped slot 216 that received thehorizontal bar system 104. By reinforcing or bulking up the area of thewall about the U-shaped slot 216, splaying of the head 110 when force isapplied to the set screw 214, in order to lock the anchor system 102, isavoided. The head 110 can use a number of shapes to be reinforced inorder to prevent splaying. The exemplary embodiment of FIGS. 1, 2,includes a pitched roof shape as seen in the top view looking down ondistal end 212 of the head 110. In particular, the wall about theU-shaped slot 216 is thickened, while the portion of the head distalfrom the U-shaped slot can be less thick if desired in order to reducethe bulk and size of the head 110 and, thus, give the head 110 a smallerprofile relative to the bone and tissue structures when implanted in apatient. Further, the small profile allows greater freedom of motion ofthe system 100 as described below. Also, it is to be understood that dueto the design of the anchor system 102, as described above, the head 110can be shorter and, thus, stand less prominently out of the bone whenthe bone screw 108 in implanted in a spine of a patient for example.

Freedom of Motion of the Embodiments of the Anchor System of theInvention

In order to accommodate embodiments of the horizontal rod systems 104 ofthe invention, to allow greater freedom in placing the horizontal rodsystems and the anchor systems 102 relative to, for example, the spineof a patient, and to provide for a smaller implanted profile in apatient, the anchor system 102 includes a number of degrees of freedomof motion. These degrees of freedom of motion are depicted in FIGS. 9,9A, 10, 10A, and 11, 11A.

FIG. 9 establishes a frame of reference including a longitudinal axis xwhich is along the longitudinal length of the bone screw 108, a y axisthat extends perpendicular to the x axis, and a lateral axis z which isperpendicular to both the x axis and the y axis and extends outwardlyfrom and parallel to the pin 190 of the yoke 180 of the anchor system102. As depicted in the figures and, in particular, FIGS. 9, 9A, thesystem 100 due to the embodiments as disclosed herein is able to havethe head 110 rotate about the z axis from about 80 degrees to about zerodegrees and, thus, in line with the x axis and from the zero degreeposition to about 80 degrees on the other side of the x axis.Accordingly, the head is able to rotate about 160 degrees about the zaxis relative to the bone screw 108. As seen in FIGS. 10, 10A the head110 is able to tilt about 0.08 inches (2 mm) relative to and on bothsides of the x axis. Accordingly, the head 110 can tilt from about 12degrees to zero degrees where the head 110 is about parallel to the xaxis and from zero degrees to 12 degrees about the y axis and on theother side of the x axis. Thus, the head can tilt through about 24degrees about the y axis. As can be seen in FIGS. 11, 11A, the head 110can swivel for a total of about 40 degrees about the x axis. Withrespect FIG. 11A, the head 110 can swivel about the x axis from about 20degrees to one side of the z axis to zero degrees and from zero degreesto about 20 degrees on the other side of the z axis. The head is able tosubstantially exercise all of these degrees of freedom at once and,thus, can have a compound position relative to the bone screw bysimultaneously moving the head within the ranges of about 160 degreesabout the z axis (FIG. 9), about 24 degrees from the y axis (FIG. 10)and about 40 degrees about the x axis (FIG. 11A).

Thus, with respect to FIGS. 9, 9A the range of motion in the axial planeis about 180 degrees or about 90 degrees on each side of the centerline.In FIGS. 10, 10A the range of motion in the Caudal/Cephalad orientationis about 4 mm or about 2 mm on each side of the centerline or about 24degrees or about 12 degrees on each side of the centerline. In FIGS. 11,11A the range of motion in the coronal plane is about 40 degrees orabout 20 degrees on each side of the centerline.

FIGS. 12, 13 depict yet another embodiment of the anchor system 102 ofthe invention where elements that are similar to elements of otherembodiments and have similar reference numbers.

As can be seen in FIG. 13, this embodiment includes a lower cradle orcompressor element 220 that is similar to the cradle or compressorelement 220 of the embodiment of FIG. 7 with the head 110 similar to thehead 110 as seen in FIG. 7. The compression sphere 200 is similar to thecompression sphere 200 in FIG. 7 with the compression sphere including aplurality of slits provided about the axis of rotation 238 of the sphere200. In this embodiment, the slits 202 have openings that alternatebetween facing the north pole of the axis of rotation of the sphere 200and facing the south pole of the axis of rotation of the sphere 200.Alternatively, the slits can be provided in the sphere and have noopening relative to the north or south pole of the axis of rotation ofthe sphere 200. Still further, the slits can open relative to only oneof the north or south poles.

In the embodiment of FIGS. 12, 13, there is also an upper cradle orcompressor element 240 which is positioned adjacent to the set screw 214(see also FIG. 7). The upper cradle or compressor element 240 has agenerally cylindrical body which can slide in the cylindrical bore ofthe head 110 with an upper end having fingers 242 extending therefrom.The fingers 242 can spring over a bore formed in the lower surface ofthe set screw 214 in order to retain the cradle 240 relative to the setscrew 214 and to allow the cradle 240 to rotate relative to the setscrew 214. The lower surface of the cradle 240 includes a concavesurface 244 which can mate with a horizontal rod 114, 116 in order tolock the rod relative the head 110 and the head 110 relative to the bonescrew 108. If desired, the concave surface 244 can be roughened toassist in locking the system 100.

Further, in FIGS. 12, 13, a retaining ring 246 is depicted. Theretaining ring can be force fit over the outer surface 218 of the head110, or pop over and snap under a ridge 248 at the distal end 212 of thehead 110, or can have internal threads that mate with external threadslocated on the outer surface of the 218 of the head 110. With the anchorsystem 102 in place in a patient and with the horizontal rod 114, 116received in the anchor system, before the set screw 214 is tightened inorder to lock the horizontal rod and the anchor system, the retainingring 246 can be attached to the head 110 in order to prevent splaying ofthe head 110 as the set screw 214 locks the system 110.

Further embodiments of the anchor system 102 which can side load thehorizontal rods 114, 116 are seen in FIGS. 14, 15, and 16, where similarelements from other embodiments of the anchor system are given similarnumeral references. With respect to the embodiment in FIG. 15, the headside wall 224 includes a lateral or side opening 250 which communicateswith the cylindrical bore 210 which is located in head 110. The lateralor side opening preferably extends more than 180 degrees about the outersurface of the head. The side opening 250 includes a lip 252 and theside opening extends down below the lip into communication with thecylindrical bore 210 and follows the outline of the concave surface 228of the cradle 220. Accordingly, a horizontal rod 114, 116, can bepositioned through the side opening 250 and urged downwardly intocontact with the concave surface 228 of the cradle 220. In thisembodiment the cradle 220 includes a downward projecting post 254. Also,this embodiment does not include a compression sphere, and instead thepin 190, which can have a larger diameter than a pin 190 in otherembodiments, comes in direct contact with the post 254 when the setscrew 112 locks the anchor system 100. If desired the pin 190 can have aroughened surface 256 to assist in the locking of the anchor system 100.As is evident from FIGS. 14, 15, 16, as this embodiment has a sideloading head 110, the distal end of the head is a fully cylindricalwithout communicating with any lateral U-shaped slots of the otherembodiments. Accordingly, this embodiment does not include any retainingring or reinforced areas that can be used to prevent splaying.

FIG. 17 depicts yet another embodiment of the anchor system 102 that hasa lateral or side loading head 110. In this embodiment, a compressioncylinder 258 is placed over the pin 190. Such a compression cylinder 258may offer less freedom of motion of the anchor system 100 with addedstability. The compression cylinder 258 can slide along the longitudinalaxis 260 of the pin 190, if desired. The head 110 can rotate about thepin 190 and the compression cylinder 258. The head 110 can also slide ortranslate along the longitudinal axis 260 of the pin as well as thelongitudinal axis of the compression cylinder 258. Compression cylinder258 has slits 262 that can be configured similarly as the slits 202 ofthe other embodiments of the anchor system 100 described and depictedherein.

FIG. 18 depicts still another embodiment of the anchor system 100 thathas a lateral or side loading head 110. This embodiment includes acompression sphere 200 provided over a pin 190 which is similar to theother compression spheres 200 depicted and described herein.Accordingly, this embodiment has the freedom of motion described withrespect to the other embodiments which use a compression sphere.

It is to be understood that although each embodiment of the anchorsystem does not necessarily depict all the elements of anotherembodiment of the anchor system, that one of ordinary skill in the artwould be able to use elements of one embodiment of the anchor system inanother embodiment of the anchor system.

Embodiments of the Horizontal Rod System of the Invention

Embodiments of the horizontal rod system 104 of the invention includethe embodiments describes above, in addition to the embodiments thatfollow. An aspect of the horizontal rod system 104 is to isolate theanchor system 102 and reduce the stress and forces on the anchor system.This aspect is accomplished by not transmitting such stresses and forcesplaced on the horizontal rod system by, for example, flexion, extension,rotation or bending of the spine to the anchor system. This aspect thusmaintains the integrity of the placement of the anchor system in, forexample, the spine and prevents loosening of the bone screw or bone hookof the anchor system. In addition, various horizontal rod systems can beused to control the rigidity, stiffness and/or springiness of thedynamic stabilization system 100 by the various elements that comprisethe horizontal rod system. Further the horizontal rod system can be usedto have one level of rigidity, stiffness and/or springiness in onedirection and another level in a different direction. For example, thehorizontal rod system can offer one level of stiffness in flexion of thespine and a different level of stiffness in extension of the spine.Additionally, the resistance to lateral bending can be controlled by thehorizontal rod system. Select horizontal rod systems allow for moreresistance to lateral bending with other select horizontal rod systemsallow for less lateral bending. As discussed below, placement of thevertical rods also effects lateral bending. The more laterally thevertical rods are placed, the more stiff the embodiment is to lateralbending.

As is evident from the figures, the horizontal rod system connects tothe heads of the anchor system without the vertical rod systemconnecting to the heads. Generally, two anchor systems are secured toeach vertebral level with a horizontal rod system connected between thetwo anchor systems. This further ensures that less stress and force isplaced on the anchor systems secured to each level and also enablesdynamic stability of the vertebra of the spine. Accordingly, movement ofthe vertebra relative to each other vertebra, as the spine extends,flexes, rotates and bends, is stabilized by the horizontal rods and theentire system 100 without placing excessive force or stress on theanchor system as there are no vertical rods that connect the anchorsystems of one vertebra level with the anchor system of anothervertebra.

With respect to FIG. 19 through FIG. 25 another embodiment of thehorizontal rod system 304 of the dynamic stabilization system 300 isdepicted as used with an anchor system 102 of the embodiment depicted inFIG. 1. Also shown in FIGS. 19, 19A, is the vertical rod system 306. Thehorizontal rod system 304 includes first and second horizontal rods308,310. It is to be understood that FIG. 19A shows a second image ofonly the horizontal rod 308 in a first undeployed position and that FIG.19 shows a deployed position with the horizontal rod 308 connected withvertical rods 306 and, thus, the entire system 300.

The horizontal rod 308 includes first and second aligned end rods 312,314 which are connected together with an offset rod 316 located betweenthe first and second end rods 312, 314. In this embodiment, thehorizontal rod 308 looks much like a yoke with the offset rod joiningeach of the end rods 312, 314 with a curved section 318, 320. At thejunction of the first end rod 312 and the offset rod 316 is a first bore322 which is aligned with the first end rod 312, and at the junction ofthe second end rod 314 and the offset rod 316 is a second bore 324 whichis aligned with the second end rod 314 and, thus, aligned with the firstend rod 312. Positioned in and extending from the first bore 322 is afirst deflection rod or loading rod 326 and positioned in and extendingfrom the second bore 324 is a second deflection rod or loading rod 328.As with the other deflection rods or loading rods, preferably deflectionrods or loading rods 324, 328 are made of a super elastic material suchas, for example, Nitinol (NiTi) and the rest of system 300 is comprisedof titanium, stainless steel, a biocompatible polymer such as PEEK orother biocompatible material. In addition to Nitinol or nickel-titanium(NiTi), other super elastic materials include copper-zinc-aluminum andcopper-aluminum-nickel. However, for biocompatibility thenickel-titanium is the desired material. The super elastic material hasbeen selected for the deflection rods as the stress or force/deflectionchart for a super elastic material has a plateau where the force isrelatively constant as the deflection increases. Stated differently, asuper elastic rod has a load (y) axis/deflection (x) axis curve whichhas a plateau at a certain level where the load plateaus or flattens outwith increased deflection. In other words, the rod continues to deflectwith the load staying constant at the plateau. In one embodiment, theload plateau is about 250 Newtons to about 300 Newtons. It is to beunderstood that the plateau can be customized to the needs of thepatient by the selection of the type and composition of the superelastic material. For some patients, the plateau should be lower, and,for others, the plateau should be higher. Accordingly, and, for example,at the plateau, additional force is not put on the anchor system 102and, thus, additional force is not put on the area of implantation ofthe bone screw 108 and the surrounding bone of the spine where the bonescrew 108 is implanted. The deflection rods or loading rods 326, 328 areforce fit, screwed, welded, or glued into the bores 322, 324 as desired.

The first and second deflection rods or loading rods 326, 328 extendfrom the respective bores 322, 324 toward each other and are joined by aY-shaped connector 330. The Y-shaped connector 330 includes a base 332which has opposed and aligned bores 334, 336 that can receive thedeflection rods or loading rods 326, 328 in a manner that preferablyallows the Y-shaped connector to pivot about the longitudinal axisdefined by the aligned first and second arms that preferably end inthreaded bores 342, 344 that can receive the threaded ends of thevertical bar system 306 as described below. Just behind the threadedbores 342, 344 are recesses 346, 348 (FIG. 24) which are shaped toaccept the offset rod 316 with the horizontal rod 308 in the undeployedconfiguration depicted in FIG. 19A. In the undeployed configuration, thehorizontal rod 308 can be more easily implanted between the tissues andbones of the spine and, in particular, guided between the spinousprocesses. Once the first horizontal rod 308 is implanted, the Y-shapedconnector 330 can be deployed by rotating it about 90 degrees or asrequired by the anatomy of the spine of the patient and connected withthe vertical rod system 306.

The second horizontal rod 310 is similar to the second horizontal rod116 of the embodiment of FIG. 1. This second horizontal rod 310 ispreferably comprised of titanium or other biocompatible material andincludes first and second mounts 350, 352 which can receive the ends ofthe vertical rod system 306. The mounts 350, 352 include respectiverecesses 354, 356 which can receive the vertical rods 358, 360 of thevertical rod system 306. The mounts 350, 352 also include tabs 362, 364which can capture the vertical rods 358, 360 in the respective recesses354, 356. The tabs 362, 364 can be secured to the mounts 350, 352 withscrews or other appropriate fastening devices.

The first and second vertical rods 358, 360 are preferably comprised oftitanium or other biocompatible material and include a threaded end anda non-threaded end. The threaded end can be formed on the end of the rodor threaded elements can be force fit or glued to the end of thevertical rods 358, 360. Once the first and second horizontal rods aredeployed in the patient, the first and second vertical rods can bescrewed into or otherwise captured by the Y-shaped connector 330 of thefirst horizontal bar 308 and the first and second vertical rods can becaptured or otherwise secured to the second horizontal bar 310.

FIGS. 26, 27, and FIGS. 28, 29 depict yet more alternative embodimentsof the horizontal rod systems of the invention. The horizontal rod 370in FIG. 26, 27 is similar to the horizontal rod 118 in FIG. 1.Horizontal rod 370 includes a mount 372 which has bores that can receivefirst and second deflection rods or loading rods 374, 376 which arepreferably made of a super elastic material. At the ends of the firstand second deflection rods or loading rods 374, 376 are connectors whichinclude a tab having a threaded bore therethrough. The connectors can beused to connect vertical rods to the deflection rods or loading rods.

FIGS. 28, 29 depict a horizontal rod 380 with first mount 382 and secondmount 384. Each of the mounts 382, 884, includes a bore that issubstantially parallel to the horizontal rod 380. First and seconddeflection rods or loading rods 386, 388 extend respectively from thebores of the first and second mounts 382, 382. In the embodimentdepicted the deflection rods or loading rods 386, 388 are parallel tothe horizontal rod 380 and are directed toward each other.Alternatively, the deflection rods or loading rods 386, 388 can bedirected away from each other. In that configuration, the mounts 382,384 would be spaced apart and the deflection rods or loading rods wouldbe shorter as the deflection rods or loading rods extended parallel toand toward the ends of the horizontal rod 380.

FIGS. 30, 31, 32 depict yet another embodiment of the horizontal rodsystem 390 of the invention which is similar to the horizontal barsystem 104 as depicted in FIG. 1. Horizontal bar system 390 includestapered deflection rods or loading rods 392, 394. The deflection rods orloading rods are tapered and reduce in diameter from the mount 396toward the ends of the horizontal rod 390. As previously discussed thedeflection rods or loading rods can taper continuously or in discretesteps and can also have an decreasing diameter from the ends of thedeflection rods or loading rods towards the mount 396. In other words, areverse taper than what is depicted in FIG. 30. Connected to thedeflection rod or loading rods 392, 394 are the vertical rods 402, 404.The vertical rods 402, 404 are connected to the deflection rods orloading rods 392, 394 as explained above.

The conically shaped or tapered deflection rods or loading rods can beformed by drawing or grinding the material which is preferably a superelastic material. The tapered shape of the deflection rods or loadingrods distributes the load or forces placed by the spine on the systemevenly over the relatively short length of the deflection rods orloading rods as the rods extend from the central mount outwardly towardthe ends of the horizontal rod. In this embodiment, in order to beoperatively positioned relative to the spine and between the anchorsystems, the deflection rods or loading rods are less than half thelength of the horizontal rods.

FIG. 30 depicts the vertical rods 402, 404 in undeployed positions thatare about parallel to the horizontal rod 390 and with the vertical rods402, 404 directed away from each other and toward the respective ends ofthe horizontal rod 390. In this position the horizontal rod 390 can bemore conveniently directed through the bone and tissue of the spine and,for example, directed between the spinous processes to the implantposition. Once in position, the vertical rods 402, 404 can be deployedso that the vertical rods are parallel to each other and about parallelto the horizontal rod 390 as depicted in FIG. 31. Accordingly, thisembodiment can be inserted from the side of the spine in the undeployedconfiguration depicted in FIG. 30 and then the vertical rods can berotated or deployed by about 90 degrees (from FIG. 30 to FIG. 31) eachinto the coronal plane of the patient. The vertical rods are also freeto rotate about 180 degrees about the deflection rods and in thesagittal plane of patient. This allows this embodiment to conform to thedifferent sagittal contours that may be encountered relative to thespine of a patient. The deflection rods or loading rods are rigidlyconnected to the horizontal rod allowing for an easier surgicaltechnique as sections of the spine and, in particular, the spinousprocesses and associated ligaments and tissues do not have to be removedin order to accommodate the implantation system 100. The moving actionof the system, and, in particular, the flexing of the deflection rodsand the motion of the vertical rods connected to the deflection rods orloading rods, takes place about the spinous processes and associatedtissues and ligaments, and, thus, the spinous processes do not interferewith this motion. Further, having the horizontal rods more lateral thancentral also allows for a more simple surgical technique through, forexample, a Wiltse approach.

To assist in implantation, a cone 406 can be slipped over the end of thehorizontal rod 390 and the vertical rod 402 to assist in urging thetissues and bone associated with the spine out of the way. Once thehorizontal rod is implanted the cone 406 can be removed. The cone 406includes an end 408 which can be pointed or bulbous and the cone 406 hasan increasing diameter in the direction to the sleeve 410 portion of thecone 406. The sleeve can be cylindrical and receive the end of thehorizontal rod and the end of the deflection rod or loading rod 402.

FIG. 32 depicts how the connectors 412, 414 are secured to therespective deflection rods 392, 394. The deflection rods have flanges,such as spaced apart flange 416, 418 on the deflection rod 392. Theconnectors 412, 414 can snap over and be retained between respectivepairs of flanges.

FIG. 33 depicts yet another embodiment of the horizontal rod system 430of the invention. The horizontal rod system 430 includes horizontal rod432 which is preferably comprised of a super elastic material such asNitinol. The horizontal rod 432 includes a generally central platform434, and on each side of the central platform 434 are first and secondupwardly facing scallops or recesses 436, 438. On each side of theupwardly facing scallop or recess 436 are downwardly facing scallops orrecesses 440, 442. On each side of the upwardly facing scallop or recess438 are downwardly facing scallops or recesses 444, 446. The platform434 accepts a connector for connecting the horizontal rod to verticalrods (FIG. 40) as will be explained below, and the scallops 436, 440,442 on one side of the platform 434 act as a spring and the scallop 438,444, 446 on the other side of the platform 434 acts as a spring. Thesesprings assist the platform in carrying the load that the spine canplace on the horizontal rod and isolate the anchor systems 102 from thatload. That isolation has the advantage of preventing loosening of theanchor system as implanted in the patient. It is to be understood thatby varying the pattern of the scallops, that the stiffness or rigidityof the horizontal bar can be varied and customized for each patient.Fewer scallops will generally result in a more stiff horizontal bar andmore scallops will generally result in a less rigid horizontal bar.Additionally, the stiffness can be different depending on the directionof the force that is placed on the horizontal bar depending on theorientation and location of the scallops. For the embodiment depicted inFIG. 33, with the scallops 436, 438 pointed upward to the head of apatient and the scallops 440, 442, 444, 446 pointed downward toward thefeet of a patient, the horizontal bar is stiffer in extension and lessstiff in flexion. It is noted that in this embodiment the rod is of auniform diameter, although the diameter can be non-uniform as, forexample, being larger where the platform 434 is and tapering to the endsof the horizontal rod 432, or having a large diameter at the ends of thehorizontal rod 432, tapering to a smaller diameter at the platform 434.In this embodiment with a substantially uniform diameter, the scallopsare formed within the uniform diameter. In other forms, the scallops aremolded into the horizontal rod or machined out of the preformedhorizontal rod. With this configuration, the horizontal rod is moreeasily inserted into the spine and between bones and tissues of thespine. Further, this horizontal rod can be more easily delivered to thespine through a cannula due to the substantially uniform diameter. Forpurposes of forming the scallops a machining technique known as wireelectric discharge machining or wire EDM can be used. Thus, an approachfor shaping the super elastic material is through wire EDM followed byelectro-polishing. Additionally, the super elastic material in this andthe other embodiments can be cold rolled, drawn or worked in order toincrease the super elastic property of the material.

In this embodiment, the deflection takes place almost exclusively in themiddle portion of the horizontal rod and principally at the platform andspring thus relieving the load or force on the ends of the horizontalrod and on the anchor system/bone interface.

Accordingly, in this preferred embodiment, there are two superiorscallops pointing upwardly having a relatively gentler radius comparedto the tighter radii of the inferior scallops pointing downwardly. It isto be understood that in this preferred embodiment, the inferiorscallops are not symmetrical the way the superior scallops are. Thelateral most cuts in both of the most lateral inferior scallops aresteep and not radiused. These cuts allow the rod to bend at these pointsenhancing the spring effect. The ratio of the radii of the superiorscallop to the inferior scallop in this preferred embodiment is two toone. The result is to create two curved and flat (in cross-section)sections, one on each side of the platform and these two flat sectionsin this preferred embodiment have about the same uniform thickness.Again, in this embodiment, the scallops and the platform is formed intoan otherwise uniformly diametered cylindrical rod. Accordingly, none ofthese formed elements in this preferred embodiment extend beyond thediameter of the rod. In this preferred embodiment, the diameter of thehorizontal rod is about 4 mm.

If desired, the rod could be bent in such a way that the platform and/orthe scallops extend outside of the diameter of the cylindrical rod.However that configuration would not be as suitable for implantationthrough a cannula or percutaneously as would the horizontal rod as shownin FIG. 33 and described above.

It is to be understood that to have enhanced flexibility, that thetorsion rod and connector elements used in the horizontal rod embodimentof FIG. 1 can be used with the horizontal rod of FIG. 33. In thisembodiment (FIG. 47), the connector is secured to the platform of thehorizontal rod of FIG. 33 with the two deflection rods or loading rodsextending toward the ends of the horizontal rod of FIG. 33 and aboutparallel to that horizontal rod.

Another embodiment of the horizontal rod 433 is depicted in FIG. 33A. Inthis embodiment the horizontal rod 433 is similar to the horizontal rodin FIG. 33 with the exception that the platform and scallops arereplaced with a reduced diameter central potion 448. Each end of thecentral portion 448 gradually increases in diameter until the diameteris the full diameter of the ends of the horizontal rod 433. Thisembodiment can be formed of a super elastic material and ground to thereduced diameter shape from a rod stock of the super elastic material.The rod stock could also be drawn to this shape. Generally after suchoperations the horizontal rod would be electro polished. In thisembodiment, a connector such as the connector shown in FIG. 40 could beused to connect vertical rods to preferably the middle of the centralportion 448.

FIGS. 34A, 34B, 34C depict yet an alternative embodiment of a horizontalrod 280 such as horizontal rod 116 as shown in FIG. 1 that is meant torigidly hold the vertical rods secured thereto. The mounts 282, 284formed in this horizontal rod 280 include a body that can be formed withthe rod 280. The mounts are then provided with a movable capture arm286, 288 that have recesses, which capture arms are formed out of themount preferably using a wire EDM process that leaves the capture armstill connected to the horizontal rod with a living hinge. Eccentricheaded set screws 290, 292 are mounted on the horizontal bar. Withvertical rods captured in the recesses of the capture arms, theeccentric set screws can be turned to urge the capture arms against theliving hinge, and thereby capturing the vertical rods in the recesses ofthe capture arms.

FIG. 40 depicts a dynamic stabilization system 450 that uses thehorizontal rod system 454 of the invention. The system 450 additionallyuses the anchor system 102 as depicted in FIG. 1 and the otherhorizontal rod 310 as depicted in FIGS. 19, 34. A connector 452 issecured to the platform 434 of the horizontal rod 454 and vertical rodsare connected to the connector and to the other horizontal rod 310. InFIG. 40 for the horizontal rod 454, the scallops are formed by bending abar and not by forming the scallops in a straight horizontal bar asdepicted in the horizontal bar 432 of FIG. 33. The horizontal rod 430 ofFIG. 33 could also be used in the embodiment of FIG. 40.

FIG. 35 depicts an alternative embodiment of a horizontal rod system 460of the invention. Horizontal rod system 460 includes a horizontal rod462 with a central platform 464 and first and second spring regions 466,468 located on either side of the platform 464. Extending outwardly fromeach spring region are respective ends of the horizontal rod 462. Thespring regions include coils that are wound about the longitudinal axisof the horizontal rod 462. If desired, the entire horizontal rod 462 canbe comprised of a rod wound around a longitudinal axis with the platform464 and the ends of the horizontal rod being more tightly wound and/orwith a smaller diameter and the spring regions 466, 468 more looselywound and/or with a larger diameter. Such a horizontal rod 462 canpreferably be comprised of super elastic material such as Nitinol oralternatively titanium or other biocompatible material whichdemonstrates the ability to flex repeatedly.

FIG. 36 depicts yet another alternative embodiment of a horizontal rodsystem 480 which includes first and second horizontal rods 482, 484which can be flat rods if desired. The horizontal rods 482, 484, includespring region 494, 496. In the spring region the horizontal rod isformed into an arc, much like a leaf spring. Located at the ends and atthe central platform 486 and between the horizontal rods 482, 484 arespacers 488, 490, 492. The spacers are glued, bonded, welded orotherwise secured between the first and second horizontal rods 482, 484in order to form the horizontal rod system 480. This system 480 can becomprised of super elastic materials or other materials that arebiocompatible with the patient.

FIG. 37 depicts another embodiment of the horizontal rod system 500including a horizontal rod 502. In this embodiment, recesses 504 areformed in the horizontal rod in order to define the stiffness of thehorizontal rod 502. This system can be formed of a super elasticmaterial or other biocompatible material.

FIG. 38 depicts still another embodiment of the horizontal rod system520 of the invention with a horizontal rod 522. The horizontal rod 522includes dimples 524 distributed around and along the horizontal rod522. As this other embodiment, depending on the distribution of thedimples, the stiffness of the horizontal rod 522 can be determined.Further is more dimples are placed on the lower surface than on theupper surface, when placed in a patient, the horizontal rod 522 wouldtend to be stiffer in extension and less stiff in flexion. Thishorizontal rod 522 can also be made of a super elastic material or otherbiocompatible material.

FIG. 39 depicts another embodiment of the horizontal rod system 530 ofthe invention which has a horizontal rod 532 which is similar to thehorizontal rod 432 of FIG. 33 and, thus, similar elements will numberwith similar numbers. In addition, the ends 534, 536 of the horizontalrod 532 are curved so as to create hooks that can fit around portions ofthe vertebra so as to secure the horizontal rod 532 to the vertebra. Inthis embodiment, preferably the rod is comprised of super elasticmaterial or other biocompatible material. In order to implant the rod,the hooks at ends 534, 536 are sprung open and allowed to spring closedaround the vertebra. An anchor system which includes a hook (asdiscussed above) could be used with this system.

FIGS. 39A, 39B are similar to FIG. 39. In FIGS. 39A, 39B, a horizontalrod 532 is held in place relative to the spine by two anchor systems102. The anchor systems are similar to the anchor systems depicted inFIG. 1. The anchor systems 102 include an anchor or bone screw 108 orbone hook 109 with spikes 111 (FIG. 39B), as well as the head 110 intowhich the horizontal rod is received. A set screw 112 secures thehorizontal rod relative to the anchor systems.

FIG. 41 depicts another embodiment of the dynamic stabilization system540 of the invention. This embodiment includes side loading anchorsystems 542 as described above, although top loading anchor systemswould also be appropriate for this embodiment. In this embodiment thehorizontal rods 544, 546 are preferably comprised of a polymer such asPEEK and mounted on the horizontal rods 544, 546 are first and secondconnectors 548, 550. Vertical rods 552 and 554 are connected to thefirst and second connectors 548, 550 at points 556 with screws, rivetsor other devices so that the connection is rigid or, alternatively, sothat the vertical rods 552, 554 can pivot or rotate about the points. Asthe horizontal rods are comprised of PEEK, the system tends to be morerigid than if the rods were comprised of a super elastic material.Rigidity also depends on the diameter of the rod.

Embodiments of the Vertical Rod System of the Invention

Embodiments of vertical rod systems of the invention such as verticalrod system 106 are presented throughout this description of theinvention. Generally, the vertical rod systems are comprised of verticalrods that can be pivoted or inserted into position after the horizontalrods are deployed in the patient. The vertical rods are preferablyconnected to the horizontal rods and not to the anchor systems in orderto reduce the forces and stress on the anchor systems. The vertical rodsare connected to the horizontal rod systems, which horizontal rodsystems include mechanisms as described herein that reduce the forcesand stresses on the anchor systems. The vertical rods can generally becomprised of titanium, stainless steel, PEEK or other biocompatiblematerial. Should more flexibility be desired, the vertical rods can becomprised of a super elastic material.

Embodiments of Alternative Multi-Level Dynamic Stabilization Systems forthe Spine

FIGS. 42 and 43 depict multi-level dynamic stabilization systems 560,580. Each of these systems 560, 580 are two level systems. All of thesesystems use anchor systems as described herein. In system 560 of FIG. 42the middle level horizontal rod 562 is secured to a vertebra andincludes a horizontal rod system 104 having first and second deflectionrods or loading rods such as that depicted in FIG. 4, whereby a firstpair of vertical rods 564 can extend upwardly from horizontal rod systemand a second pair of vertical rods 566 can extend downwardly from thehorizontal rod system. The vertical rods that extend upwardly areconnected to an upper horizontal rod 568 such as depicted in FIG. 34 andthe vertical rods that extend downward are connected to a lowerhorizontal rod 568 such as depicted in FIG. 34. The upper horizontal rod568 is secured with anchor systems to a vertebra located above thevertebra to which the middle level horizontal rod 562 is secured. Thelower horizontal rod 570 is secured with anchor systems to a vertebralocated below the vertebra to which the middle level horizontal rod 562is secured. This embodiment offers more stability for the middle levelvertebra relative to the upper and lower vertebra while allowing forextension, flexion, rotation and bending relative to the middle levelvertebra.

FIG. 43 depicts another multi-level dynamic stabilization system 580.All of these systems use anchor systems as described herein. In system580 of FIG. 43, the middle level horizontal rod 582 is secured to avertebra and includes a horizontal rod such as that depicted in FIG. 34.The upper and lower horizontal rods 586, 590 can be similar to thehorizontal rod 114 including the deflection rods or loading rods anddeflection rod or loading rod mount depicted in FIG. 3. Vertical rodsare pivotally and rotationally mounted to the upper and lower horizontalrods 586, 590 and, respectively, to the deflection or loading rodsthereof and are also rigidly mounted to the middle level horizontal rod582. The upper horizontal rod 586 is secured with anchor systems to avertebra located above the vertebra to which the middle level horizontalrod 582 is secured. The lower horizontal rod 590 is secured with anchorsystems to a vertebra located below the vertebra to which the middlelevel horizontal rod 582 is secured. This embodiment offers more dynamicstability for the upper and lower vertebra relative to the middle levelvertebra while allowing for extension, flexion, rotation and bendingrelative to the middle level vertebra. Alternatively, the middle levelhorizontal rod 582 has four mounts instead of the two mounts depicted inFIG. 34 or FIG. 34A so that a first pair of vertical rods 588 can extendupwardly from a lower horizontal rod 590 and a second pair of verticalrods 566 extending downwardly from the upper horizontal rod 586, can besecured to the middle level horizontal rod 582.

Embodiments of Spine Fusion Systems of the Invention

FIGS. 44, 45 depict one and two level systems that are more preferablyused for fusion. The system 600 depicted in FIG. 44 resembles the systemdepicted in FIG. 41. When PEEK is used for the horizontal rods 602, 604,the system is substantially rigid and can be used in conjunction withspine fusion. For example, this system can be used with the placement ofbone or a fusion cage between vertebra to which this system is attached.In fusion, bone can be placed between the vertebral bodies or,alternatively, fusion can be accomplished by placing bone in the valleyson each side of the spinous processes. The horizontal rods 602, 604 analso be comprised of titanium, or other biocompatible material and beused for spine fusion. For this embodiment, the vertical rods 606 can berigidly attached to the horizontal rods through the use of a horizontalrod with mounts, as depicted in FIG. 34, so that the vertical rods 606do not move or pivot with respect to the horizontal rods.

FIG. 45 depicts a two level system 620 that is more preferably used fora two level fusion. Each level can use an anchor system for exampledescribed with respect to anchor system 102 of FIG. 1. The horizontalrods 622, 624, 626 are can be similar to the horizontal rod in FIG. 34with either two vertical rod mounts for the upper and lower horizontalrods 622, 626 or four vertical rod mounts for the middle levelhorizontal rod 624. For this embodiment, the vertical rods 628, 630 canbe rigidly attached to the horizontal rods through the use of ahorizontal rod with mounts as depicted in FIG. 34 so that the verticalrods 628, 630 do not move or pivot with respect to the horizontal rods.Vertical rods 628 extend between the upper and middle horizontal rods622, 624, and vertical rods 630 extend between the middle and lowerhorizontal rods 624, 626. The system 620 depicted in FIG. 44 resemblesthe system depicted in FIG. 41, but with respect to three levels. WhenPEEK is used for the horizontal rods 622, 624, 626, the system issubstantially rigid and can be used in conjunction with spine fusion.For example, this system can be used with the placement of bone or afusion cage between vertebra to which this system is attached. Bone canalso be placed along the valleys on either side of the spinous processesfor this system. The horizontal rods 622, 624, 626 can also be comprisedof titanium, PEEK or other biocompatible material and be used for spinefusion.

With respect to FIG. 45, to ease the transition to a one level fusedarea of the spine this two level system can be modified by replacing thehorizontal rod 622 with a horizontal rod 115 (FIGS. 45A, 45B), which ismuch like horizontal rod 104 with deflection or loading rods 118, 120 ofFIG. 1. This embodiment is depicted in FIG. 45A. Thus, fusion isaccomplished between the two lower horizontal rods 117 which rods arelike those depicted in FIG. 34, or like horizontal rods 116 in FIG. 1,and made of, preferably, titanium, and flexibility is provided by theupper horizontal rod 115 that is like horizontal rod 114 with deflectionor loading rods that are shown in FIG. 1. Accordingly, there is moregradual transition from a healthier portion of the spine located abovehorizontal rod 115 through horizontal rod 115 to the fused part of thespine located between horizontal rod 624 and horizontal rod 606 of FIG.45 or between the horizontal rods 117 (FIG. 45A).

Method of Implantation and Revised Implantation

A method of implantation of the system in the spine of a human patientis as follows.

First the vertebral levels that are to receive the system areidentified. Then the anchor systems are implanted, generally two anchorsystems for each level. The anchor systems can be implanted using acannula and under guidance imaging such as x-ray imaging. Alternatively,the anchor system can be implanted using traditional spinal surgerytechniques. Then the horizontal rods are inserted and secured to theanchor systems. The horizontal rods can be inserted laterally through acannula or with an incision and the use of, for example, a lead-in cone.Alternatively, the horizontal rods can be inserted using traditionaltechniques when the anchor systems are implanted. Thereafter, thevertical rods can be pivoted, rotated or placed into communication withand secured to the appropriate horizontal rod.

Should a dynamic stabilization system such as system 100 be initiallyimplanted and then should there be a desire to make the system morerigid or to accomplish a fusion, the system 100 can be revised byremoving the horizontal rod 104 that includes the deflection rods orloading rods and replace it with a horizontal rod 106 which has thevertical rod mounts (FIG. 34) and is thus substantially more rigid. Thusa revision to a fusion configuration can be accomplished with minimaltrauma to the bone and tissue structures of the spine.

Materials of Embodiments of the Invention

In addition to Nitinol or nickel-titanium (NiTi) other super elasticmaterials include copper-zinc-aluminum and copper-aluminum-nickel.However for biocompatibility the nickel-titanium is the preferredmaterial.

As desired, implant 100 can be made of titanium or stainless steel.Other suitable material includes by way of example onlypolyetheretherketone (PEEK), polyetherketoneketone (PEKK),polyetherketone (PEK), polyetherketoneetherketoneketone (PEKEKK), andpolyetheretherketoneketone (PEEKK). Still, more specifically, thematerial can be PEEK 450G, which is an unfilled PEEK approved formedical implantation available from Victrex of Lancashire, GreatBritain. (Victrex is located at www.matweb.com or see Boedekerwww.boedeker.com). Other sources of this material include Gharda locatedin Panoli, India (www.ghardapolymers.com).

As will be appreciated by those of skill in the art, other suitablesimilarly biocompatible thermoplastic or thermoplastic polycondensatematerials that resist fatigue, have good memory, are flexible, and/ordeflectable have very low moisture absorption, and good wear and/orabrasion resistance, can be used without departing from the scope of theinvention.

Reference to appropriate polymers that can be used in the spacer can bemade to the following documents. These documents include: PCTPublication WO 02/02158 A1, dated Jan. 10, 2002, entitled“Bio-Compatible Polymeric Materials;” PCT Publication WO 02/00275 A1,dated Jan. 3, 2002, entitled “Bio-Compatible Polymeric Materials;” andPCT Publication WO 02/00270 A1, dated Jan. 3, 2002, entitled“Bio-Compatible Polymeric Materials.”

The foregoing description of preferred embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many embodiments were chosenand described in order to best explain the principles of the inventionand its practical application, thereby enabling others skilled in theart to understand the invention for various embodiments and with variousmodifications that are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claims andtheir equivalents.

1. An anchor assembly comprising: a anchor body with an anchor; ananchor head including a stirrup including a yoke extending from theanchor body and a shaft positioned across the yoke; a saddle mountingelement located on said shaft; a saddle including a port that isreceived about said saddle mounting element; and a set that can locksaid saddle mounting element against said shaft in order to positionsaid saddle relative to said anchor body.
 2. The anchor assembly ofclaim 1 wherein said saddle mounting element is a sphere having a borethat is received over said shaft.
 3. The anchor assembly of claim 1wherein said saddle mounting element is a cylinder having a bore that isreceived over said shaft.
 4. The anchor assembly of claim 1 wherein saidsaddle mounting element is a sphere having a bore that is received oversaid shaft; and said port allows said saddle to pivot about said sphereand to rotate about said sphere prior to said set locking said saddlerelative to said anchor body.
 5. The anchor assembly of claim 4 whereinsaid saddle mounting element allows said saddle to translate along saidshaft with said saddle mounting element.
 6. The anchor assembly of claim2 wherein said saddle mounting element has one or more slots.
 7. Theanchor assembly of claim 1 wherein said saddle mounting element is acylinder having a bore that is received over said shaft; and said portallows said saddle to rotate about said cylinder prior to said setlocking said saddle relative to said anchor body.
 8. The anchor assemblyof claim 7 wherein said saddle mounting element allows said saddle totranslate along said shaft with said saddle mounting element.
 9. Theanchor assembly of claim 3 wherein said saddle mounting element has oneor more slots.
 10. An anchor assembly comprising: a anchor body with ananchor; an anchor head including a stirrup including a yoke extendingfrom the anchor body and a shaft positioned across the yoke; a spheremounted on said shaft; a saddle including a cavity that is receivedabout said sphere; and a set that can lock said sphere against saidshaft in order to position said saddle relative to said anchor body. 11.The anchor assembly of claim 10 wherein said sphere has a bore that isreceived over said shaft; and said cavity allows said saddle to pivotabout said sphere and to rotate about said sphere prior to said setlocking said saddle relative to said anchor body.
 12. The anchorassembly of claim 11 wherein said sphere allows said saddle to translatealong said shaft with said sphere.
 13. The anchor assembly of claim 10wherein said sphere allows said saddle to translate along said shaftwith said sphere.
 14. The anchor assembly of claim 10 wherein saidsphere has one or more slots.
 15. The anchor assembly of claim 10wherein said sphere has a roughened surface.
 16. The anchor assembly ofclaim 1 wherein said sphere has a roughened surface.
 17. An anchorassembly comprising: a anchor body with an anchor; an anchor headincluding a stirrup including a yoke extending from the anchor body anda shaft positioned across the yoke; a cylinder mounted on said shaft; asaddle including a cavity that is received about said cylinder; and aset that can lock said cylinder against said shaft in order to positionsaid saddle relative to said anchor body.
 18. The anchor assembly ofclaim 17 wherein said cylinder has a bore that is received over saidshaft; and said cavity allows to rotate about said cylinder prior tosaid set locking said saddle relative to said anchor body.
 19. Theanchor assembly of claim 18 wherein said cylinder allows said saddle totranslate along said shaft with said cylinder.
 20. The anchor assemblyof claim 17 wherein said sphere allows said saddle to translate alongsaid shaft with said cylinder.
 21. The anchor assembly of claim 17wherein said sphere has one or more slots.
 22. The anchor assembly ofclaim 17 wherein said sphere has a roughened surface.